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It's common for me to want a unique slug based on a user supplied name of an object. Following the pattern outlined at ​djang-tips-auto-populated-fields, it's easy to get the field populated without user intervention. However, by setting the slug field in the save() method the field isn't validated and thus unique=True restrictions aren't checked. I wrote the following code to attempt to pick slugs which are unique within a particular model. It's certainly not ideal (it suffers from race condition as well as potential for pounding a database with lots of small queries until it finds a good slug field), but it works for my small/mid-sized apps.

Feel free to suggest improvements to 'wam-djangowiki spam@…' (remove the ' spam' from the address there).

def SlugifyUniquely(value, model, slugfield="slug"):
"""Returns a slug on a name which is unique within a model's table
This code suffers a race condition between when a unique
slug is determined and when the object with that slug is saved.
It's also not exactly database friendly if there is a high
likelyhood of common slugs being attempted.
A good usage pattern for this code would be to add a custom save()
method to a model with a slug field along the lines of:
from django.template.defaultfilters import slugify
def save(self):
if not self.id:
# replace self.name with your prepopulate_from field
self.slug = SlugifyUniquely(self.name, self.__class__)
super(self.__class__, self).save()
Original pattern discussed at
http://www.b-list.org/weblog/2006/11/02/django-tips-auto-populated-fields
"""
suffix = 0
potential = base = slugify(value)
while True:
if suffix:
potential = "-".join([base, str(suffix)])
if not model.objects.filter(**{slugfield: potential}).count():
return potential
# we hit a conflicting slug, so bump the suffix & try again
suffix += 1